Producing maleic acid by oxidation of cyclohexane



June 28, 1949. 2,474,334

PRODUCING MALEIC ACID BY OXIDATION OF CYCLOHEXANE A. J. SHMIDL Filed April 10, 1947 %ondoniu or Catalystcutolyn Oxygon Contchkq Scporutor 415ml g MW INVENTOR.

Patented June 19.49

c m-:1) STATE YCLO Albert J. Shmidl, Houston Tex assignor, by

mesne assignments, to Standard Oil Development Company, Elizabeth, N.

of Delaware J a corporation Application April 10, 1947, sennfno. 740,563

1 Claim. (Cl. 260-533).

aldehydes, carboxylic acids and other products of oxidation.

It has long been known that oxygenated compounds of the nature mentioned above may be produced from hydrocarbons by subjecting the hydrocarbons to proper conditions of temperature, pressurefcatalyst, and in the presenceof an oxidizing atmosphere to obtain these compounds. It has been the practice in the prior .art to' employ various types of catalyst suchas the oxides and salts of titanium, vanadium, chromium, manganese, molybdenum and cerium as catalyst in the production of .the oxygenated compounds such as the alcohols, aldehydes, carboxylic'acids' and the like. I

The feed stocks employed in the prior art processes have comprised the naphthenes, parafllnes;

and high molecular weight hydrocarbons such as wax andthe like. These feed stocks have been admixed with air or other oxy en contai n gases and subjected to temperature and pressure conditions either catalytically or non-catalytically to obtain useful oxygenated organic compounds. The prior art catalytic processes, however, have the disadvantage that the catalyst is subject to an induction period in which there i a period of operating time at the outset at which useful products are not obtained and serious and economic loss is suffered. The non-catalytic processes suffer by virtue of higher temperatures being necessary and yields lower than the. catalytic processes.

It is, therefore, the main object of the present invention to provide a process in which useful products may be produced at theoutset with no useful operating time lost prior to-obtaining commercial quantities of the desired product;

. 2 it hydrocarbon and oxidizing medium, for example air, in proper proportions.

Briefly, the present invention may be described as embodying a process in which two or more catalyst cases containing oxidation catalyst are provided andwhich the hydrocarbon in a, heated vaporous condition is passed through a first case at a temperature higher than oxidizing conditions but without the oxidizing medium andtheeflluent from this case then mixed with the-oxidizing medium and passed to a second catalyst case at temperatures under which oxidation occurs. The eflluen't from the second catalyst case includes oxygenated products which .are then routed through a. heater or condenser, depending upon the products obtained, and from thence to a separator where a separation is made among the gasiform materials, oil phase, and water phase. It Willithllgbe apparent-that a process is provided in which the hydrocarbon is passed in series through one case, mixed with an oxidizing medium, and then passed through a second case. When the second case becomes spent or shows a decreased activity for oxygenating hydrocarbons, the flow may be reversed and the hydrocarbon passed through-the second case and the mixture of hydrocarbon and oxygen containing Another objec't oi the present'invention is to condition or'pretreat an oxidation catalyst to allow the catalyst to have enhancedactivity for oxygenation of hydrocarbons-to useful oxygen ated organic compounds.

The objects of lthe present invention may be achieved by subjecting an oxidation catalyst such as an oxide or saitof the elements such as titanium, vanadium, chromium, "manganese, molybdenum, cerium" and the like to the action oi a heated vaporous hydrocarbon under nonoxidizing conditions prior to contacting the catalyst at oxidizing conditions with a mixture of the gaspassed through the first case. a

The invention will be further. illustrated by reference to the drawing in which the single figure is a ilow sheet of one method of practicing the invention. I 4

Referring now to the drawing, numerals I l and i2 describe-respectively catalyst cases containing an oxidation catalyst, for example-vanadium pentoxide deposited on 8 to 10, mesh pumice. A hydrocarbon in a heatedvaporous condition is introduced by way. of manifold i3 into line ll controlled by valve 15 and thence into catalyst case I I, in which the catalyst is designated by the shaded portion 16. The heated vaporous hydrocarbon passes downwardly through the catalyst case II and discharges therefrom by 'way of line H, controlled by valve 18 into manifold [9, wherein it is admixed with an oxygen containing gas such as air. The admixture of oxygen 00D! taining gas and heated hydrocarbons is then routed by manifold l9 through line 2!), controlled by valve 2i, upwardly through catalyst case I! containing a catalyst similar to that contained in catalyst case II and which is indicatedby'the shaded portion 22. The admixture passes upwardly through the catalyst 22 and under conditions maintained sumcient to produce substantial quantities of oxygenated hydrocarbons.

The eiluent from the catalyst case it issues therefrom through line It, controlled by valve 2|, and discharges into manifold II; which connects by way of line 26 into condenser-or heater 21, which is provided with suitable cooling or heat ing means indicated by arrow 28 for adjusting the temperature downwardly or upwardly as desired. The oxygenated eiliuent passes through condenser or heater 21 and discharges by line 2! into a separator 3|, which is provided with a heating or cooling means 3i, to maintain the contents or the separator in a substantially liquid condition sumcient for mobility and to allow the contents thereof to be pumped.

The separator 3| is provided with a line 32 for releme of any gaseous compounds which may accumulate therein and which results from the oxidation reaction. line I! for separation and removal of an oil phase containing unreacted hydrocarbon and oxygenated products, and line It for removal of a water phase containing water and oxygenated compounds soluble therein.

When the catalyst 22 in catalyst case I! becomes spent or shows a decreased activity for oxidizing hydrocarbons. the flow throu h the system may be reversed by closing valve II in line H, opening valve II in line It. closing valve 24 in line 28 and opening valve 81 in line it. Under these conditions the hydrocarbon passes throu h manifold it through open valve II in line 38 downwardly through catalyst case ii, the eflluent issuing through line 20, controlled by valve 2!. passes through manifold II; is admixed with oxygen introduced into the system by line II. and

passes upwardly through line". controlled byvalve ll into catalyst case H which has become activated or conditioned by the hydrocarbon passing downwardly therethrough prior to reversal of the operation. and the eiiluent issues from the catalyst case H by line 8|. controlled by valve 31, into manifold II, and thence as described through line 28. condenser or heater 21, line to separator II for separation of the products'as has been described previously.

It will be apparent from the foregoing description that a continuous operation has been provided in which a reactivated or conditioned catalyst is maintained at all times for oxidation of the hydrocarbons. It will also be obvious that no operating time is lost in conditioning or pretreating the catalyst by proceeding according to the foregoing description.

While not shown in the drawin it may be deslrable to provide. in manifold is between lines I1 and II, a cooling means so that the temperature of the eiiiuent from either catalyst case II or catalyst case I! may becooled to the oxidation temperature before admixing it with the free oxygen containing was admitted into the system through line ll. This'cooling means may be a suitable heat exchanger. device and the temperaoxidize cyclohexane to malelc acid. The catalyst was ineflectlve in catalyzing this oxidation.

The catalyst prepared as described in the foregoing description was then pretreated with vaporizedcyclohexane and it was found that the pretreatment gave a catalyst of appreciably improved activity and selectivity to maleic acid. The pretreatment operation was conducted by heating the catalyst and the cyclohexane to about 800 F., whereby the cyclohexane was in vaporous condition. and passing it over the catalyst for about four hours. Subsequent to the treatment and before the oxidation was conducted, the hydrocarbons were swept from the catalyst bed by nitrogen and the mixture of hydrocarbon and oxygen was then passed over the catalyst, which had been conditioned, to obtain maleic acid.

The data in the following table compares results obtainable without pretreating the catalyst and with pretreating the catalyst at operations conducted at 600 F., ratios of air to hydrocarbon varying between 120 and 134:1, at contact in the neighborhood of 3to 3.9 seconds.

It will'be apparent from the foregoing data that pretreating increased the maleic acid conture differential may be employed to sup ly heat when necessary to heater or condenser 21 or to the contents of separator It.

The invention will be further illustrated by the following examples:

An oxidation catalyst was prepared by adding 30 parts or ammonium vana'date to 100 parts of silica hydrogel. The vanadate in the mixture was decomposed with nitric acid and the total mixture which had been treated with nitric acid was washed free of acid with water; the acid-free.

material was dried and then calcined for 3 hours version twelve-fold where the air-hydrocarbon ratio was substantially :1. In the case where the air-hydrocarbon ratio was 134:1, the increase was only about iive-fold. which nevertheless is substantial.

Additional runs were then made on the catalyst produced as described above in which. the catalyst was pretreated with cyclohexane vapors at about 800 F. and runs were made employing this pretreated catalyst to catalyze the oxidation of-a mixture of cyclohexane and air. The data from these runs are presented in the following table:

It will be apparent from the foregoing data in Table II that a substantial improvement was also obtained at higher air to hydrocarbon ratios by employing a pretreated catalyst over that obtained when an untreated catalyst was employed as in conventional practice.

It will also be apparent from these runs which.

in this case, were successive 5-hour runs, that the activity of the catalyst in each instance showed a gradual decline over that obtained in the outset until the yield was about 65% of the yield obtained during the first 5-hour period of operation with the catalyst treated in accordance with the present invention. By periodically reversing the flow and passing hydrocarbon only through one of a plurality of cases and passing hydrocarbon and oxygen mixture through at least a second of I a plurality of cases containing oxidation catalyst,

oxygenated compounds without interruption.

While the invention has been described by reference to passing the hydrocarbons serially through one of a plurality of catalyst cases and then admixing it with oxygen containing gas and then passing the mixture through another of a plurality of cases, it will be apparent to the skilled worker that other methods may be used to obtain the same end. For example, a catalyst case may be so designed that air may be injected after hydrocarbon has contacted a portion of the catalyst, such as about half of the catalyst, followed by a reversal in direction of hydrocarbon flow periodically as the catalyst in contact with the oxygen containing mixture loses its activity. This will maintain the catalyst activity at a high level. A preferred procedure, however, is that described in which a plurality of catalyst cases i is employed in series with the hydrocarbon entering the first of the plurality of cases and the oxygen containing hydrocarbon mixture entering the second of the plurality of catalyst cases.

The invention has been described by reference to the oxidation of cyclohexane. It is intended that the invention not be limited or restricted to cyclohexane or other naphthenic hydrocarbons. It is equally applicable to oxidation of paraffinic hydrocarbons such as propane, butane, pentane, hexane, heptane and the like. Similarly, other naphthenic hydrocarbons besides cyclohexane may be oxidized as stated before. As exemplary of the other naphthenic hydrocarbons, may be mentioned cyclopentane and the higher members of the same homologous series.

The temperatures to be employed in the practice of the present invention will generally include those temperatures found useful in oxidizing hydrocarbons. The temperature at .which the oxidation will be conducted may range from 500 to 000 F., depending on the hydrocarbon being oxidized. It will be generally desirable to conduct the pretreating operation at a temperature substantially greater than'the oxidation operation. For example, as shown when oxidizing cyclohexane with maleic acid, the pretreatment may be conducted at a temperature of 800 F. and the oxidation at a temperature of 600 F. Generally it will be desired to conduct the pretreating operation at a temperature at least 50 F. greater than the temperature at which the oxidation is conducted. However, when oxidation is conducted at temperatures approaching 1000 F. the pretreatment may be conducted at a similar temperature, provided the contact is short enough to minimize cracking reactions.

The nature and objects of the present invention having been fully illustrated and described, what I wish to claim as new and useful and to secure by Letters Patent is:

A method for oxidizing cyclohexane which includes the steps of forming a bed of vanadium pentoxide, heating said bed to a temperature or approximately 800 F., passing a heated vaporous stream of cyclohexane at a temperature of about 800 F. over said bed for a time sufllcient to activate said bed, forming an admixture of cyclohexane with an'oxygen-containing gas, reducing the temperature of said activated bed from about 800 F. to approximately 600? F. and subsequently passing said admixture at a temperature of approximately 600 F. over said activated bed to obtain improved yields of maleic acid from the cyclohexane in said admixture. ALBERT J. SHMIDL.

REFERENCES CITED The following referenlces are of record in the fiie of this patent:

OTHER REFERENCES Lubarsky et al.: Comptes Rendus, .(U. S. S. 1%.), vol. 29, pages 575-6 (1940). Copy in 260-668 D. 

